This invention pertains to inkjet inks, more specifically to pigmented inkjet inks containing crosslinked polyurethane dispersoid binders, which are particularly suitable for textile printing.
Inkjet recording is a printing method wherein droplets of ink are ejected through fine nozzles to form letters or figures on the surface of recording media. Inks used in such recording are subject to rigorous demands including, for example, good dispersion stability, ejection stability, and good fixation to media.
Both dyes and pigments have been used as colorants for inkjet inks. While dyes typically offer superior color properties compared to pigments, they tend to fade quickly and are more prone to rub off. Inks comprising pigments dispersed in aqueous media are advantageously superior to inks using water-soluble dyes in water-fastness and light-fastness of printed images.
Pigments suitable for aqueous inkjet inks are in general well known in the art. Traditionally, pigments are stabilized by dispersing agents, such as polymeric dispersants or surfactants, to produce a stable dispersion of the pigment in the vehicle. Other additives to the ink modify the ink to match the needs for the target printed system, which includes the media.
Digital printing methods such as inkjet printing are becoming increasingly important for the printing of textiles and offer a number of potential benefits over conventional printing methods such as screen printing. Digital printing eliminates the set up expense associated with screen preparation and can potentially enable cost-effective short run production. Inkjet printing furthermore allows visual effects, such as tonal gradients and repeat of printed patterns, that cannot be practically achieved with a screen printing process. Especially in the case of the production of pattern originals it is possible to respond to a change in requirements within a significantly shorter period of time.
Suitable such digital printing systems for textiles are disclosed, for example, in commonly owned US20030128246 and US20030160851, the disclosures of which are incorporated by reference herein for all purposes as if fully set forth. Even as inkjet hardware improvements are made to increase printing speeds, adoption of inkjet printing in the textile industry will be impeded if methods to also improve colorfastness are not found.
U.S. Pat. No. 4,597,794 discloses inkjet ink formulations suitable for textile, with the ink formulation dispersion medium containing a polymer having both an ethylenically unsaturated carboxylic acid substituent as a hydrophilic portion and an aromatic ring substituent as a hydrophobic portion. Wash fastness was described as excellent for fabrics were imaged with this ink and set by heating at 150° C. for five minutes.
U.S. Pat. No. 5,897,694 discloses inkjet ink formulations comprising, as an additive, a transition metal chelate. These inks are said to provide improved wash fastness.
U.S. Pat. No. 5,958,561 discloses an ink/textile combination wherein the textile is pretreated with a crosslinkable thermoplastic polymer and then imaged with an aqueous ink and cured at temperatures of 100-190° C. Improved washfastness was reported.
U.S. Pat. No. 6,146,769 discloses an ink/textile combination wherein a water-soluble interactive polymer, in at least one of the inks or on the textile, is said to help bind the particulate colorant and provide wash fastness.
Japanese laid-open patent Hei 9-143407 discloses an inkjet ink with thermoset resin which is imaged on fabric and fixed by heating at 130° C. The image is said to be water resistant.
Japanese laid open patent Hei 8-283636 discloses an inkjet ink with specified resin emulsions having high Tg. Fabric imaged with this ink is fixed at elevated temperature to provide washfastness.
WO03/029362 discloses a pigmented inkjet ink suitable for textiles comprising an emulsion polymer and a crosslinking agent which is suitable for cross linking the emulsion polymer. The disclosure suggests that the use of the described crosslinking agent improves dry and wash fastness.
U.S. Pat. No. 6,034,154 discloses polymer fine particles, each polymer fine particle containing a colorant. One of the candidate polymers making up the polymer portion of the fine particle is described as a crosslinked polyurethane.
U.S. Pat. No. 6,136,890 describes pigmented inks that contain pigments and polyurethane dispersants that stabilize the pigments. The pigment is dispersed by the polyurethane via dispersing techniques used to achieve a stabile pigment dispersion.
US20030105187 describes a water-based pigmented ink for use in inkjet printing (on paper and transparencies media). The ink consists of a pigment and a latex, of which uncrosslinked polyurethanes are listed as candidate latexes.
WO03/029318 describes polyurethane block copolymers as dispersants for inks. These polyurethanes are crosslinked prior to inversion (addition of water to produce the polyurethane dispersion) not during or after inversion. There is also crosslinking derived from the added melamine crosslinker which is only effective at high temperatures and/or acidic conditions that occur at the time of the textile treatments after printing.
The disclosures of all of the above-identified publications are incorporated by reference for all purposes as if fully set forth.
A disadvantage of inkjet printing, in particular inkjet printing with pigmented ink, is inkjet printed fabrics are particularly susceptible to color removal by abrasion and thus have poor durability. Furthermore, another disadvantage of inkjet printing, in particular inkjet printing with pigmented ink is that inkjet printed fabrics do not tolerate washing conditions required for textiles. The printed colors both fade upon washing and during the wash the colors can be undesirably transferred to other fabrics in the wash or to the washing machine parts.
Still, there is need in the art for improved durability of inkjet images on textile, especially in cases where the colorant is pigment.
It is thus an object of this invention to provide inkjet printed textiles with improved durability and colorfastness especially as a result of laundering.